Generally Magnetic North or Auto Magnetic, depending on your GPS device should work best for what we do. My personal preference is to also set the map orientation to the direction of travel, rather than maintaining north as the "top" of the map. That way as you move in a direction, the top of the map on screen shows the map in that direction and the map moves from top to bottom of the screen.

The website GPS Tracklog is full of good information regarding GPS units, as well as links to deals, etc. In the case of Garmin units, you don't need to spend the money to buy their topo maps, which are crap, but you can download some great maps for free.

I like to keep the North Reference point up at all times, that way I know where I am on the whole map rather than try to orient the map in my mind to know what direction I am going and where the waypoint is supposed to be. Everybody has thier preference but this would be my recommendation. I say this because when communicating to other members, you will need to know direction based on N, E, S, or West from your position.